Thank you Dan
Dan Weston wrote: > > If you find it tedious to pass parameters that never change, remember > that you can access symbols defined in the enclosing environment > (closure), freeing you from "passing it on" each time: > > filterAlpha :: (a -> Bool) -> [a] -> [a] > filterAlpha f = filterAlpha' > where filterAlpha' [] = [] > filterAlpha' (x:xs) > | f x = x : (filterAlpha' xs) > | otherwise = (filterAlpha' xs) > > As far as the primed version filterAlpha' is concerned, f is a global > symbol. The argument list is just used for values that vary. > > This will be your friend if the parameter list starts to stack up with > more and more "reference" or "environment" inputs. It is also easier to > see that f never changes if it is defined in only one spot. > > Later, when you study monads you will notice the same pattern in the > Reader monad, where the technique is even more valuable. > > Dan Weston > > Alexteslin wrote: >> >> filterAlpha :: (a -> Bool) -> [a] -> [a] >> filterAlpha f [] = [] >> filterAlpha f (x:xs) >> |f x = x : filterAlpha f xs -- corrected >> |otherwise = filterAlpha f xs -- corrected > > > _______________________________________________ > Haskell-Cafe mailing list > [email protected] > http://www.haskell.org/mailman/listinfo/haskell-cafe > > -- View this message in context: http://www.nabble.com/filterFirst-tf4131377.html#a11790806 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. _______________________________________________ Haskell-Cafe mailing list [email protected] http://www.haskell.org/mailman/listinfo/haskell-cafe
